From: Erik Veenstra <erikveen@...>
Date: 2008-08-01T22:54:10+09:00
Subject: About circular dependencies in RubyGems (the library). And about the order in $".

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Hi,

There's a circular dependency in RubyGems. I mean in the
library itself, not in the collection of gems.

Try this:

 $ RUBYOPT= ruby -e 'require "rubygems/exceptions"'
 /usr/local/lib/ruby/site_ruby/1.8/rubygems/remote_fetcher.rb:19:
uninitialized constant Gem::Exception (NameError)
         from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/spec_fetcher.rb:4:in `require'
         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/spec_fetcher.rb:4
         from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/source_index.rb:10:in `require'
         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/source_index.rb:10
         from /usr/local/lib/ruby/site_ruby/1.8/rubygems.rb:767:in `require'
         from /usr/local/lib/ruby/site_ruby/1.8/rubygems.rb:767
         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/exceptions.rb:1:in
`require'
         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/exceptions.rb:1
         from -e:1:in `require'
         from -e:1

The main script requires rubygems/exceptions.rb, which requires
rubygems.rb, which requires rubygems/exceptions.rb (which is
skipped since it has already been required (although is not yet
listed in $"...)) and rubygems/source_index.rb, which requires
rubygems/spec_fetcher.rb, which requires
rubygems/remote_fetcher.rb, which defines class FetchError as a
subclass of Gem::Exception, which fails since Gem::Exception
has not yet been defined (rubygems/exceptions.rb is still on
line 1).

This causes RubyScript2Exe to fail. RubyScript2Exe sequentially
requires every entry in $" when tracing the application. It's
essentially doing this:

 $ export RUBYOPT=
 $ ruby -r $THE_LIBRARY -e 'puts $"' | xargs ruby -e 'ARGV.each{|x| puts x ;
require x}'

Which works for all libraries on my machine, except for
RubyGems.

The essence of the problem is a bit nasty: a library is only
added to $" _after_ it's executed, so the order in which the
libraries appear in $" is reversed. Well that's true for
indirect dependencies (app requires a, which requires b, which
requires c ==> $" == ["c.rb", "b.rb", "a.rb"], but not for
sequential dependencies (app requires a, b and c ==> $" ==
["a.rb", "b.rb", "c.rb"]).

Question: Is it possible to investigate the exact order in which
libraries are required correctly? Obviously $" won't work. We
can't wrap Kernel#require either, since you'll miss the
libraries which are required on the command line or in $RUBYOPT.

Any ideas/suggestions/comments?

Thanks.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

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